Geobacter sulfurreducens can grow with oxygen as a terminal electron acceptor

Geobacter sulfurreducens, previously classified as a strict anaerobe, tolerated exposure to atmospheric oxygen for at least 24 h and grew with oxygen as the sole electron acceptor at concentrations of 10% or less in the headspace. These results help explain how Geobacter species may survive in oxic subsurface environments, being poised to rapidly take advantage of the development of anoxic conditions.     

Arginine and lysine residues as NADH-binding sites in NADH-nitrate reductase from spinach.

Chemical modifications of spinach leaf nitrate reductase, and its 28,000 M(r) fragment with phenylglyoxal, 2,3-butanedione and pyridoxal phosphate reduce the catalytic activity of the enzyme. The kinetics of the modification indicate a rapid inactivation followed by a slower rate of inactivation. NADH-nitrate reductase, NADH-cytochrome c reductase and NADH-ferricyanide reductase activities of the nitrate reductase complex are inactivated at a faster rate when compared to the loss of FMNH2-nitrate reductase and reduced methyl viologen (MVH)-nitrate reductase activities. NADH protects the inactivation of NADH-ferricyanide reductase activity of the 28,000 M(r) fragment of nitrate reductase. These data suggest that nitrate reductase contains active sites of arginine and lysine residues that are involved in the NADH binding site of the enzyme.     

Heme synthesis in yeast does not require oxygen as an obligatory electron acceptor

In a previous paper (Krawiec, Z., Biliński, T., Schüller, C. & Ruis, H., 2000, Acta Biochim. Polon. 47, 201-207) we have shown that catalase T holoenzyme is synthesized in the absence of oxygen after treatment of anaerobic yeast cultures with 0.3 M. NaCl, or during heat shock. This finding suggests that heme moiety of the enzyme can either be formed de novo in the absence of oxygen, or derives from the preexisting heme pool present in cells used as inoculum. The strain bearing hem1 mutation, resulting in inability to form delta-aminolevulinate (ALA), the first committed precursor of heme, was used in order to form heme-depleted cells used as inocula. The cultures were supplemented with ALA at the end of anaerobic growth prior the stress treatment. The appearance of active catalase T in the stressed cells strongly suggests that heme moiety of catalase T is formed in the absence of oxygen. This finding suggests the necessity to reconsider current opinions concerning mechanisms of heme synthesis and the role of heme as an oxygen sensor.     

Formate oxidation by Wolinella recta ATCC 33238 with oxygen as electron acceptor

Abstract The formate oxidizing capacity of Wolinella recta ATCC 33238 was studied in relation to growth under anaerobic and microaerobic conditions. Three distinct activities could be recognized: (a) cyanide-insensitive H₂O₂-producing oxidation of formate; (b) peroxidation of formate (H₂O₂-consuming); (c) oxidation of formate via an electron transport chain with oxygen as the electron acceptor. The contribution of these different formate oxidizing components during the growth of W. recta was dependent on the extent of aeration. It is suggested that due to the relative increase in overall H₂O₂ formation at higher oxygen tensions growth of W. recta appears possible only under anaerobic and microaerobic conditions.     

Sequence-based screening and characterization of cytosolic mandelate oxidase using oxygen as electron acceptor

Sequence-based screening was carried out to find a type of cytosolic mandelate oxidase that converted l-mandelate to phenylglyoxylate using oxygen as the final electron acceptor. The sequence features of the cytosolic mandelate oxidase were summarized, and were used in the screening process. Mandelate oxidases from Streptomyces coelicolor (Hmo_SC) and Amycolatopsis orientalis (Hmo_AO) were screened and then they were heterologously expressed and characterized. At pH 7.3 40 °C, the Hmo_AO showed k_cat and K_m values of 140 min⁻¹ and 10.2 mM, the Hmo_SC showed k_cat and K_m values of 105.1 min⁻¹ and 2.06 mM. The Hmo_SC was thermal stable and retained its 90% activity at 60 °C for up to 5 h, while Hmo_AO lost most of its activity at this temperature. The Hmo_SC could effectively catalyze the conversion of l-mandelate to phenylglyoxylate at higher temperature using oxygen as the final electron acceptor.     

Reactive oxygen species (ROS) generated by cyanobacteria act as an electron acceptor in the biocathode of a bio-electrochemical system

The enhanced electricity generation in a biocathode bio-electrochemical system (BES) with Microcystis aeruginosa IPP as the cathodic microorganism under illumination is investigated. The results show that this cyanobacterium is able to act as a potential cathodic microorganism under illumination. In addition, M. aeruginosa IPP is found to produce reactive oxygen species (ROS) in its growth in the BES. ROS, as more competitive electron acceptors than oxygen, are utilized prior to oxygen. The BES current is substantially reduced when the ROS production is inhibited by mannitol, indicating that the ROS secreted by the cyanobacterium play an important role in the electricity generation of such a biocathode BES. This work demonstrates that the ROS released by cyanobacteria benefit for an enhanced electricity generation of BES.     

Photosynthetic oxygen exchange in C4 grasses: the role of oxygen as electron acceptor

C₄ grasses of the NAD‐ME type (Astrebla lappacea, Eleusine coracana, Eragrostis superba, Leptochloa dubia, Panicum coloratum, Panicum decompositum) and the NADP‐ME type (Bothriochloa bladhii, Cenchrus ciliaris, Dichanthium sericeum, Panicum antidotale, Paspalum notatum, Pennisetum alopecuroides, Sorghum bicolor) were used to investigate the role of O₂ as an electron acceptor during C₄ photosynthesis. Mass spectrometric measurements of gross O₂ evolution and uptake were made concurrently with measurements of net CO₂ uptake and chlorophyll fluorescence at different irradiances and leaf temperatures of 30 and 40 °C. In all C₄ grasses gross O₂ uptake increased with increasing irradiance at very high CO₂ partial pressures (pCO₂) and was on average 18% of gross O₂ evolution. Gross O₂ uptake at high irradiance and high pCO₂ was on average 3.8 times greater than gross O₂ uptake in the dark. Furthermore, gross O₂ uptake in the light increased with O₂ concentration at both high CO₂ and the compensation point, whereas gross O₂ uptake in the dark was insensitive to O₂ concentration. This suggests that a significant amount of O₂ uptake may be associated with the Mehler reaction, and that the Mehler reaction varies with irradiance and O₂ concentration. O₂ exchange characteristics at high pCO₂ were similar for NAD‐ME and NADP‐ME species. NAD‐ME species had significantly greater O₂ uptake and evolution at the compensation point particularly at low irradiance compared to NADP‐ME species, which could be related to different rates of photorespiratory O₂ uptake. There was a good correlation between electron transport rates estimated from chlorophyll fluorescence and gross O₂ evolution at high light and high pCO₂.     

Microbial arsenite oxidation with oxygen,nitrate, or an electrode as the sole electron acceptor

The purpose of this study was to identify bacteria that can perform As(III) oxidation for environmental bioremediation. Two bacterial strains, named JHS3 and JHW3, which can autotrophically oxidize As(III)–As(V) with oxygen as an electron acceptor, were isolated from soil and water samples collected in the vicinity of an arsenic-contaminated site. According to 16S ribosomal RNA sequence analysis, both strains belong to the ?-Proteobacteria class and share 99% sequence identity with previously described strains. JHS3 appears to be a new strain of the Acinetobacter genus, whereas JHW3 is likely to be a novel strain of the Klebsiella genus. Both strains possess the aioA gene encoding an arsenite oxidase and are capable of chemolithoautotrophic growth in the presence of As(III) up to 10 mM as a primary electron donor. Cell growth and As(III) oxidation rate of both strains were significantly enhanced during cultivation under heterotrophic conditions. Under anaerobic conditions, only strain JHW3 oxidized As(III) using nitrate or a solid-state electrode of a bioelectrochemical system as a terminal electron acceptor. Kinetic studies of As(III) oxidation under aerobic condition demonstrated a higher V _max and K _m from strain JHW3 than strain JHS3. This study indicated the potential application of strain JHW3 for remediation of subsurface environments contaminated with arsenic.     

Preferential use of an anode as an electron acceptor by an acidophilic bacterium in the presence of oxygen

Several anaerobic metal-reducing bacteria have been shown to be able to donate electrons directly to an electrode. This property is of great interest for microbial fuel cell development. To date, microbial fuel cell design requires avoiding O(2) diffusion from the cathodic compartment to the sensitive anodic compartment. Here, we show that Acidiphilium sp. strain 3.2 Sup 5 cells that were isolated from an extreme acidic environment are able to colonize graphite felt electrodes. These bacterial electrodes were able to produce high-density electrocatalytic currents, up to 3 A/m(2) at a poised potential of +0.15 V (compared to the value for the reference standard calomel electrode) in the absence of redox mediators, by oxidizing glucose even at saturating air concentrations and very low pHs.     

Inhibition of NADH-nitrate reductase activity in cucumber leaves due to NADH oxidation

The activity of crude NADH-nitrate reductase of cucumber leaveswas not linearly related to its concentration. The enzyme fractionand crude inhibitors could be roughly separated by saturationwith (NH₄₂SO₄. Inhibition of NR activity was not prevented bytreatment of crude inhibitors with insoluble PVP, BSA and PMSF,which is serinespecific protease inhibitor. However, the inhibitionwas reduced by increasing concentrations of NADH. Crude inhibitorsshowed NADH oxidation activities when measured with or withoutelectron acceptors. Crude enzyme preparation from cucumber leavescultured with nitrate could form nitrite when only NADH wasadded. Furthermore, NADH-oxidizing activities in crude inhibitorswere fractionated into one main and one minor activity whenassayed without an electron acceptor. DCIP accelerated onlythe main NADH oxidation activity. With NR, the minor activityproduced stronger inhibition than the main one. This stronginhibition of NR activity was found to be due to the acceleratedNADH oxidation by the association of enzyme with the minor-activityfraction. The results indicate that the NR activity in cucumberleaves may be regulated by the level of NADH, but the natureof the acceleration of NADH oxidation due to association isnot known. ¹ Pressent address: Institute for Agricultural and BiologicalSciences, Okayama University, Kurashiki, Japan. Please addressrequest of riprints to H. M. ² Present address: National Research Institute of Brewing, Kitaku,Tokyo, Japan. (Received November 9, 1978; )     

Tetrachloroethylene as electron acceptor for the anaerobic degradation of benzoate

Abstract Teltrachloroethylene (PCE) was biotransformed by reductive dehalgenation under anoxic conditions with benzoate as the electron donor. The experiments were carried out under batch culture conditions with biomass from an anoxic fixed bed reactor fed with benzoate and PCE. Inhibition of methanogenesis by bromoethane-sulfonic acid (BES) resulted in a complete inhibition of benzoate degradation. Benzoate, however, was decomposed in the presence of BES if PCE was added to the cultures. With 2.8 mmol/1 PCE, that was transformed to 1.4 mmol/1 cis-1,2-dichloroethylene (DCE) and 3.8 mmol/1 chloride, 2 mmol/1 benzoate were degraded to about 3.2 mmol/1 acetate. The elimination of benzoate was directly proportional to DCE accumulation, ranging between 1:0.5 and 1:1.     

Growth of sulfate-reducing bacteria with sulfur as electron acceptor

In addition to three new isolates, six strains of representative species of sulfate-reducing bacteria were tested for their capacity to use elemental sulfur as an electron acceptor for growth. There was good growth and sulfide production by strain Norway 4 and the three isolates, two of which had been enriched with sulfur flower and one isolated from a culture with green sulfur bacteria. Slow but definite growth was observed with Desuflovibrio gigas. The type strains of Desulfovibrio desulfuricans, D. vulgaris, and Desulfotomaculum nigrificans as well as Desulfomonas pigra did not grow with sulfur. The four strains that grew well with sulfur flower were straight, nonsporulating rods and did not contain desulfoviridin.     

Oxygen as an alternative electron acceptor in the photosynthetic electron transport chain of C3 plants

This study deals with effects of oxygen on the kinetics of P(700) photoinduced redox transitions and on induction transients of chlorophyll fluorescence in leaves of C(3) plants Hibiscus rosa-sinensis and Vicia faba. It is shown that the removal of oxygen from the leaf environment has a conspicuous effect on photosynthetic electron transport. Under anaerobic conditions, the concentration of oxidized P700 centers in continuous white light was substantially lower than under aerobic conditions. The deficiency of oxygen released non-photochemical quenching of chlorophyll fluorescence, thus indicating a decrease in the trans-thylakoid pH gradient (DeltapH). Quantitative analysis of experimental data within the framework of an original mathematical model has shown that the steady-state electron flux toward oxygen in Chinese hibiscus leaves makes up to approximately 40% of the total electron flow passing through photosystem 1 (PS1). The decrease in P700+ content under anaerobic conditions can be due to two causes: i) the retardation of electron outflow from PS1, and ii) the release of photosynthetic control (acceleration of electron flow from PS2 to P700+) owing to lower acidification of the intra-thylakoid space. At the same time, cyclic electron transport around PS1 was not stimulated in the oxygen-free medium, although such stimulation seemed likely in view of possible rearrangement of electron flows on the acceptor side of PS1. This conclusion stems from observations that the rates of P700+ reduction in DCMU-poisoned samples, both under aerobic and anaerobic conditions, were negligibly small compared to rates of electron flow from PS2 toward P700+ in untreated samples.     

Methyl viologen as a preferred electron acceptor in metabolic experiments.

Widely used artificial electron acceptors, including dichlorophenol-indophenol, methylene blue, and phenazine ethosulfate, were shown to induce the nonenzymatic decarboxylation of pyruvate. This characteristic rendered these electron acceptors unsuitable for use in metabolic experiments. In contrast, methyl viologen stimulated the pentose phosphate pathway in mouse preimplantation embryos without decarboxylating pyruvate in the process. Furthermore, methyl viologen had no effect on the Embden-Myerhoff pathway and was not overtly toxic to mouse embryos. These features made methyl viologen a preferred artificial electron acceptor for metabolic studies.